Decolorization characteristics and mechanism of azo dyes by a thermophilic bacterial consortium

Abstract:

[Background] The high temperature of textile wastewater inhibits the degradation of azo dyes by microorganisms. Little is known about the degradation of azo dyes by thermophiles. [Objective] To enrich the thermophilic microbiota that can degrade azo dyes at high temperature and study their degradation potential and genomic characteristics. [Methods] We obtained a thermophilic bacterial consortium by the enrichment method and then studied its degradation characteristics by spectrophotometry. The degradation mechanism was analyzed by full-wavelength scanning, Fourier transform infrared spectroscopy (FTIR), and gas chromatography-mass spectrometry (GC-MS). The phytotoxicity of azo dyes before and after degradation was compared. The functional genes and structure were analyzed by high-throughput sequencing. [Results] A bacterial consortium (SD1) was enriched, which can degrade azo dye at 65 ℃. SD1 was mainly composed of Caldibacillus, unclassified_f__Bacillaceae, and Geobacillus. It could degrade acid red GR within pH 5.0–9.0, 50–75 ℃, dye concentration of 100–500 mg/L, and salinity of 1%–5%. Azo reductase and NADH-DCIP were the main degrading enzymes. The results of GC-MS and FTIR demonstrated that the azo bond was broken by SD1. The phytotoxicity of acid red GR decreased after degradation. The genes encoding NADH-dependent flavin mononucleotide (FMN) azo reductase and FMN-dependent reductase involved in the degradation were detected. [Conclusion] The thermophilic bacterial consortium SD1 has great potential to be applied in the treatment of high-temperature textile wastewater.

Key words:azo dye;thermophilic bacteria;decolorization;acid red GR;metagenome